On Thursday the couple posted a statement at the social networking Web site friendsorenemies.com in which they announced that they would be getting married.

"We are thrilled to share that we are happily engaged. We consider this to be a very private matter, but we wanted you to hear it straight from us," the announcement said.

Simpson began her career with a role on the hit WB series, "Seventh Heaven."

Her new album, "Bittersweet World," will be released April 22.

Wentz co-founded Fall Out Boy in 2001, and the band, for which he is also the lyricist, has built a fan base with such hit songs as "Sugar, We're Goin Down" from the 2005 album, "From Under the Cork Tree."